1. Field of the Invention
This invention relates to improved methods of reducing NOx emissions produced by a steam boiler fired by a fluid fuel and combustion air burner.
2. Description of the Prior Art
Packaged unit and other steam boilers which are fired by fluid fuel and combustion air burners are commonly used in chemical and other process installations. Such boilers include a steam drum which is provided with feed water and from which produced steam is withdrawn. In order to maintain the appropriate total dissolved solids in the boiler water and avoid scale formation, blowdown steam is withdrawn from the steam drum. The blowdown steam flow depends on the feed water quality and typically amounts to in the range of from about 1.5 to about 5% of the total steam produced by the boiler. The blowdown steam is released to the atmosphere or used to preheat the feed water and then released to the atmosphere.
In order to reduce the NOx emissions produced by the steam boilers, a portion of the produced process steam has heretofore been combined with the combustion air utilized by the steam boiler burner. This usage of process steam lowers the efficiency of the boiler or requires additional make-up water which increases the cost of operating the boiler.
Thus, there are needs for more efficient methods of reducing NOx emissions produced by steam boilers.
The present invention provides methods of reducing NOx emissions in the flue gases produced by a steam boiler fired by a fluid fuel and combustion air burner which meets the needs described above and overcomes the deficiencies of the prior art. The methods of the present invention basically comprise combining at least a portion of the blowdown steam which would otherwise be wasted with the fluid fuel utilized by the boiler. In addition, the blowdown steam can be combined with the combustion air and injected into the furnace of the boiler to reduce NOx and stabilize the flame in the furnace.
An improved method of the present invention for reducing the NOx emissions produced by a steam boiler fired by a fluid fuel and combustion air burner includes the steps of combining a portion of the flue gases produced by the boiler with the combustion air and combining a portion of the blowdown steam from the boiler with the fluid fuel.
Yet another improved method of reducing NOx emissions produced by a steam boiler fired by a fluid fuel and combustion air burner includes the steps of combining a portion of the flue gases produced by the boiler and a portion of the blowdown steam from the boiler with the combustion air and combining another portion of the flue gases and another portion of the blowdown steam with the fluid fuel
Still another improved method of the present invention for reducing. the NOx emissions produced by a steam boiler fired by a fluid fuel and combustion air burner includes the steps of withdrawing a minor portion of blowdown steam and a major portion of blowdown water containing a high level of dissolved solids from the boiler, purifying the blowdown water and recirculating it as a part of the make-up water to the boiler, combining a portion of the flue gases produced by the boiler with the combustion air and combining at least a portion of the blowdown steam from the boiler with the fluid fuel.
Thus, it is a principle object of the present invention to provide improved methods of reducing NOx emissions produced by a steam boiler fired by a fluid fuel and combustion air burner.
Other and further objects, features and advantages of the present invention will be readily apparent to those skilled in the art upon a reading of the description of preferred embodiments which follows when taken in conjunction with the accompanying drawings.